Basic Electrostatic Spray Finishing

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    Basic Electrostatic Spray Finishing 

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    Concept and Theory Training 

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    Introduction

    Welcome to Basic Electrostatic Spray Finishing , a learning module in Graco’s basic concept and

    theory sales training curriculum. Your understanding of the information in this module providesthe basis for further study of specific Graco products. Your ability to successfully promote and sell Graco’s products depends in part on how well you learn the basics and then apply this knowledge to addressing your customers’ needs for Graco equipment.

    While this curriculum best fits the requirements of Graco and distributor sales people, it will also  benefit anyone whose job function depends on knowledge of Graco’s products.

    Module Overview 

    This module introduces basic information on electrostatic spray finishing processes, including the underlying terms, concepts, and principles. You will understand how electrostatic charging can be

    used with a variety of spray finishing systems to improve spray transfer efficiency.

    How to Use This Module 

    The curriculum consists of a series of self-study modules. As the term self-study implies, you work through the materials on your own at a comfortable pace. Plan sufficient time (approximately 30 minutes) to complete at least one section of a module in a working session.

    This module combines a variety of features that make the learning process convenient and productive:

    • Learning objectives

    • Text

    • Charts and illustrations

    • Progress checks

    • Additional resources

    Learning Objectives

    Each section of materials offers a set of learning objectives. Read the objectives and use them to guide you to the most important concepts. After you finish each section and before you complete the progress check, reread the learning objectives to confirm that you understand the key concepts.

    Text

    Definitions, examples, and explanations comprise the learning module text. Read it carefully and return for review if necessary.

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    Charts and Illustrations

    An important element of any instruction is visualizing the concepts. This module contains graphics and illustrations to enhance the text material. Whenever appropriate, the module also contains charts that help you organize or summarize information.

    Progress Checks

    Progress checks are self-tests that provide reinforcement and confirm your understanding of important topics. After completing each major section of the module, return to review the objectives, and then work through each of the progress check items. Upon completion, check your answers against those provided. If you answered any incorrectly, return to the text and reread the pertinent information.

    Additional Resources

    This module may refer you to other documents or sources that expand on the concepts covered in the module. The reference will include the name of the source and how you can obtain it.

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    Introduction to Electrostatic Spray Finishing

    Learning Objectives 

    This section provides a foundation for learning about electrostatic spray finishing. The term electro- statics or electrostatic spray finishing refers to a spray finishing process in which electrical charges and electric fields are used to attract particles of atomized coating material to the target (the object to be coated). In the most common types of electrostatic systems, electrical charges are applied to the coating material and the target is grounded, creating an electric field. The charged particles of coating material are drawn by the electric field to the surface of the grounded target because of the attraction of opposing electrical charges. Other, less common types of electrostatic systems apply an electrical charge to the target and ground the coating material, or apply opposite electrical charges to the coating material and the target. After completing this introduction to electrostatic spray finishing, you will be able to:

    • Define the term electrostatics

    as it applies to spray finishing. • Discuss how electrostatic spray charging is used to improve the transfer efficiency of

    spray finishing.

    • Name several types of spray finishing systems with which electrostatics are used.

    • Recognize key terms used to discuss electrostatic spray charging.

    Why Use Electrostatic Spray Finishing? 

    Electrostatic spray charging improves the transfer efficiency of spray finishing equipment. The transfer efficiency improvements occur because the electrostatic forces help overcome other forces,

    such as momentum and air flow, that can cause the atomized materials to miss the intended target. Electrostatic methods save coating material, time, and labor. More of the material is attracted to and adheres to the target, and less material is lost in the spray booth and the surrounding environment. Electrostatic methods also lower solvent emissions into the air since less coating material is needed to coat each part.

    Types of Electrostatic Systems 

    Electrostatic spray finishing systems can be either automatic or manual.

    Automatic Electrostatic Systems

    The automatic electrostatic systems include:

    • High speed rotational (stationary or reciprocating) atomizers

    • Reciprocating discs

    • Automatic air spray, airless, air assisted airless, or HVLP spray guns

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    Key Terms 

    Figure 2 below provides definitions for many of the terms used to explain electrostatic spray charging. Review the definitions now. You can refer back to these definitions, as needed, while you proceed through this module or other training on Graco electrostatic products.

    Key Terms For Understanding Electrostatics

    Current The flow of electrons. Measured in amps, milliamps, or microamps.

    Voltage The force or pressure pushing electrons. Measured in volts or kilovolts.

    Circuit A completed (circular) electrical path that permits the flow of electrons.

    Ground Within a circuit, a connection to earth potential or true earth ground.

    Conductor Material through which electrons can easily flow.

    Resistor Material through which electrons cannot easily flow, and used to control the flow of electrons in electrical circuits. Measured in ohms or megohms.

    Insulator Non-conductive, highly resistive material that stops the flow of electrons.

    Ionization The process by which molecules gain or lose electrons.

    Generator A machine that changes mechanical energy into electrical energy.

    Alternator A generator that changes mechanical energy to alternating current.

    Power Supply A device that converts one type of electrical power to a different type of electrical power—for example, from low voltage AC to high voltage DC.

    Capacitance The storage or accumulation of electrical charges

    on a conductive surface that is insulated fromother conductive surfaces so that it will hold its electrical charge.

    Capacitor A device within an electrical circuit used to hold electrical charges.

    Transfer The percent of coating materials that reaches the target Efficiency when spraying.

    Figure 2 Key terms for electrostatics

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    Understanding Particle Charges

    Learning Objectives 

    To understand electrostatic spray charging, you must first be able to identify the types of charged particles that make up matter and explain how charged particles impact one another. After com- pleting this section on electrical charges, you will be able to:

    • Name the types of particle charges that make up matter.

    • Explain how electrically charged particles act on other particles with the same or different charges.

    • Describe the forces of electric fields.

    Dynamics Among Charged Particles 

    All matter has an electrical charge. Matter is made up of three types of electrically charged particles:

    1. Negatively charged particles have excess electrons.

    2. Positively charged particles have excess protons.

    3. Neutral particles have a balanced number of electrons and protons.

    Particles and objects with like charges repel each other, whereas particles with unlike charges attract each other. A single, isolated particle that is either negatively or positively charged will attract neu- tral particles. Charged particles are also attracted to the closest grounded surface.

    The three types of electrically charged particles are illustrated in Figure 3.

    Figure 3 Electrically charged particles

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    Negatively charged particle

    Positively charged particle Neutral particle

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    Electric Fields 

    Electric (or electrostat

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